About Lesson
Relative size of soil mineral particles
- Sand:
- Usually consists of quartz but may also contain fragments of feldspar, mica and occasionally heavy minerals viz., zircon, Tourmaline and hornblende.
- Has uniform dimensions
- Can be represented as spherical
- Not necessarily smooth and has jagged surface
- Silt:
- Particle size intermediate between sand and clay
- Since the size is smaller, the surface area is more
- Coated with clay
- Has the physico- chemical properties as that of clay to a limited extent
- Sand and Silt forms the SKELETON
- Clay:
- Particle size less than 0.002 mm
- Plate like or needle like in shape
- Belong to alumino silicate group of minerals
- Sometimes considerable concentration of fine particles which does not belong to alumino silicates. (e.g.). Iron oxide and CaCO3
- These are secondary minerals derived from primary minerals in the rock
- Flesh of the soil
- Loam:
- Loams are the best soil suited to all purposes.
- Relative proportion of soil separates/soil particles (<2mm) in a given soil mass.
- Indicates the coarseness & fineness of a soil.
- Affects physical, chemical & biological properties of a soil.
Necessary to know sizes & behavior of soil separates to understand use of soil texture
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Soil particles |
USDA system (diameter) |
ISSS system (diameter) |
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Sand |
0.05 to 2mm |
0.02 to 2mm |
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|
Silt |
0.002 to 0.05 mm |
0.002 to 0.02mm |
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|
Clay |
< 0.002mm |
< 0.002mm |
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|
Gravels |
2to 75 mm |
|
|
|
Cobbles |
75 to 250 mm |
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|
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Stones |
>250 mm |
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